Heart disease is a serious health condition affecting millions of people worldwide. One major cause of heart disease is the presence of blockages or lesions within the blood vessels that reduce blood flow through the vessels. Traditionally, surgeons have relied on X-ray fluoroscopic (planar) images to show the external shape or silhouette of the blood vessels to guide treatment. Unfortunately, using only X-ray fluoroscopic images lends a great deal of uncertainty about the exact extent and orientation of the lesion responsible for the occlusion, making it difficult to find the exact location of the stenosis for treatment. In addition, X-ray fluoroscopy is an inadequate reassessment tool to evaluate the vessel after surgical treatment.
A currently accepted technique for assessing the severity of a stenosis in a blood vessel, including ischemia-causing lesions, is fractional flow reserve (FFR). FFR is defined as the ratio of the maximal blood flow in a stenotic artery, taken distal to the lesion, to normal maximal flow. Accordingly, to calculate the FFR for a given stenosis, two blood pressure measurements are taken: one measurement distal or downstream to the stenosis and one measurement proximal or upstream to the stenosis. FFR is a calculation of the ratio of the distal pressure measurement relative to the proximal pressure measurement. FFR provides an index of stenosis severity that allows determination as to whether the blockage limits blood flow within the vessel to an extent that treatment is required. The more restrictive the stenosis, the greater the pressure drop across the stenosis, and the lower the resulting FFR. FFR measurements can be used as a decision point for guiding treatment decisions. The normal value of FFR in a healthy vessel is 1.00, while values less than about 0.80 are generally deemed significant and require treatment. Common treatment options include angioplasty, atherectomy, and stenting.
One method of measuring the pressure gradient across a lesion is to use a pressure-sensing guidewire that has a pressure sensor embedded within the guidewire itself. A user may initially position the pressure sensor of the guidewire distal to the lesion and measure the distal pressure before drawing the guidewire backwards to reposition the sensor proximal to the lesion to measure the proximal pressure. This method has the disadvantages of inaccurate pressure readings due to drift and increased susceptibility to thermal variations, high manufacturing costs, and time-consuming repositioning steps (especially in situations involving multiple lesions). Further, pressure-sensing guidewires often suffer from reduced precision and accuracy in making intravascular pressure measurements when compared to larger pressure-sensing devices, such as aortic pressure-sensing catheters.
Another method of measuring the pressure gradient across a lesion is to use a small catheter connected to a blood pressure sensor, which is often contained in a sensor housing associated with the catheter. However, this method can introduce error into the FFR measurement because as the catheter crosses the lesion, the catheter and the sensor housing themselves create additional blockage to blood flow across the lesion and contributes to a lower distal blood pressure than what would be caused by the lesion alone, which may exaggerate the measured pressure gradient across the lesion.
While the existing treatments have been generally adequate for their intended purposes, they have not been entirely satisfactory in all respects. The devices, systems, and associated methods of the present disclosure overcome one or more of the shortcomings of the prior art.